archive.worldofdragon.org

Hello everybody!

I was recovering Froglet by CRL and found something interesting.

When the game is dumped via XRoar, it works ok, but, if you take a look at the blocks, there's no end block and the last block has a CRC error. With my own program, I managed to get another data block and the end block, but couldn't fix the faulty block.

The funny thing is that my complete copy doesn't load (?I/O ERROR), but If I remove the end block and the last data block, leaving the faulty block as last block in the .cas file, the game works!

Is this some kind of copy protection?

And, what should I do from the preservation point of view? Keep both copies, as to show how such mechanism was implemented while having a working copy?

You'll find attached an image showing the blocks and crc's for both cas files (left mine, right XRoar), and both cas files.

[EDIT] When converted to .WAV, both files load on a real Dragon...

[EDIT 2] Created Froglet page in the wiki.

Yes, it is a very weak form of copy protection. The game auto-runs by overwriting the stack. The reason that it gives an I/O error is because the original code was saved to tape with an end address higher than the stack. You can easily defeat the auto-run by entering CLEAR10 before loading the game. Once loaded, entering EXEC&H5000 will then run the game as normal.

Attached below is the same game but with a more conventional RAM hook type auto-run routine added.

Its also not alone - I came across a few of these whilst converting stuff for this site...

Another one is an EOF block in the middle of the data blocks - the autorun loader ignores it - but anybody looking to hack the program may not and thus end up with missing code.

None of them were that effective...

Zephyr, your version loads beatifully on XRoar, thanks!

The funny thing is that the wav file from my cas file loads ok in XRoar, but not the cas file... The wav file also loads on a real Dragon. So I think my .cas file is ok (including the extra data block and EOF block) for preservation purposes, but then I don't know why XRoar doesn't load the .cas file right away. Could it be some minor tape handling issue?

Your .CAS file loads and auto-runs OK on MESS, PC-Dragon and T3.

Ok, thanks for testing it!

I'll put that file properly named in the uploads section then and contact Sixxie on XRoars's behaviour.

Have a nice day!